The present invention relates to a golf ball, and more specifically, relates to a golf ball with improved frictional force at the time it is hit.
It is well known that when a golf ball is hit, backspin is applied to the golf ball. If too much backspin is applied on a driver shot, the ball tends to pop up. Accordingly, in order to extend the flight distance, it is generally desired to reduce the amount of backspin. In contrast, on approach shots, the greater the amount of backspin, the easier it becomes to control the golf ball to stop at a point near the landing point. Accordingly, desired amounts of backspin are converse in driver shots and in approach shots. In addition, it is well known that the friction between the club and the ball is related to the amount of backspin.
For example, in JP 2004-201787 A, it is disclosed that the greater the loft angle of the club head, the greater the amount of backspin of the ball according to the magnitude of the frictional coefficient of the face surface. It is also disclosed therein that in contrast, for a head with a small loft angle, the greater the frictional coefficient of the face surface, the less the amount of backspin.
In order to extend the flight distance of golf balls, research has been conducted to improve the aerodynamic performance of golf balls by devising the shape of a large number of dimples formed on the surface of golf balls. For example, in JP 2005-006755 A, a configuration of a dimple is disclosed in which a protrusion is provided in the center of the bottom of a dimple so that the radius of curvature of the center protrusion satisfies a predetermined condition. In JP 2008-012300 A, a configuration of a dimple is disclosed in which a circular protrusion is provided around the center of the bottom of a dimple, the upper end surface of the protrusion is flat, and the height of the protrusion and the depth of a ring-like portion around the protrusion satisfy predetermined conditions. In JP 2011-120612 A, a configuration of a dimple is disclosed in which the sectional shape of a dimple is a wave-like curve including plural alternately arranged upward protrusions and downward protrusions.